Re: [Discuss-gnuradio] GNURadio Run with USRP2 Hangs on Execution

[Ian Buckley]

Paul, 
With (the default) 16bit complex sample format the maximum sample rate 
supported on USRP2 is 25Msps, simply because that is pretty much as much data 
as you can get over 1G Ethernet in one direction.
50Msps is supported if you use 8bit complex samples and loose some dynamic 
range.

The decimation rate must be an integer, thus 25Msps is a decimation rate of 4 
from the raw ADC converter clock of 100MHz. Also, since the receive DSP chain 
cascades 2 Halfband FIR filters (each with fixed decimation of 2) before a CIC 
filter (With arbitrary integer decimation), it is preferable to always use 
decimation rates that factor by 4 so that both half band filters are active 
which results in the flattest passband. UHD will automatically use the half 
band filters in preference to the CIC when possible with the specified 
decimation.

-Ian


On Oct 23, 2013, at 3:39 PM, Paul B. Huter <address@hidden> wrote:

> I finally got my GNURadio Python script running, but after I execute the 
> script, I get a UHD Warning about requested decimation (a few lines of text), 
> then a single 0 on a newline, and nothing. I let it run for about five 
> minutes, and my output file didn't change from 0 bytes.
> 
> I am trying to capture the entire shortwave frequency spectrum to analyze 
> later (hence the output file). I am using a sample I found online, modified 
> for GNURadio 3.7. I have set the following parameters
> 
> samp_rate = 30000000 (for 30MHz)
> tune_request = 15000000 (for the middle frequency)
> self._head = blocks.head(8, int(1000000)) (that is what the example stated to 
> use for number of samples, but I will likely change that once I verify 
> everything is working correctly)
> 
> I am not getting any errors, like I was initially before converting it all to 
> 3.7, except not doing anything for five minutes and the output file size not 
> growing.
> 
> Links to similar projects are welcome, and any feedback/help is appreciated.
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